The blood-brain barrier (BBB) is an endothelial tissue that surrounds and protects the CNS by excluding potentially toxic substances present in blood from entry into the brain while allowing selective entry of nutrients and other blood components. Unfortunately, the blood-brain barrier also prevents systemically administered protein therapeutic agents such as recombinant antibodies from entry into the CNS. Thus, the blood-brain barrier imposes a serious practical limitation on the usefulness of protein therapeutics for the treatment of CNS disorders. The present invention represents an advance in providing accessibility of the CNS for genetically encoded protein pharmaceuticals whose ability to cross the blood-brain barrier is limited.